Fuel container



June 17, 1947. HOLT 2,422,239

FUEL CONTAINER Filed Jan. 22. 1942 2 Sheets-Sheet 1 7 git/Um Harald El-Holt Jung 17, 1947. s, HOLT 2,422,239

I FUEL CONTAINER Filed Jan. 22. 1942 2 Sheets-Sheet 2 3 Q l l roZecZz'v e JoZvenZ Cover-{72 Expanding Laz er Expanding? L @2 er ReJz'JZdnZ Layer H a1- cflcl E1. H011 d? 7? 27/44 4 Patented June 17,

s PATENT OFFICE FUEL CONTAINER Harold S. Holt, Wilmington, Del., assignor to E; I.

du Pont de Nemours & Company, Del'., a corporation of Delaware Wilmington,

Application January 22, 1942, Serial No. 427,837

1 Claim. 1

of the self-sealing type.

The self-sealing containers of the kind withwhich this invention is concerned comprise an inner layer more or less inert to the contained liquid, one or more expanding layers capable of mechanical expansion to close perforations,. or subject to rapid swelling when exposed to the contained liquid, and in some instances, an outer protective layer which may be of flexible or of rigid material. When the container wall is pierced the hole in the expanding layer or layers closes to stop the leak. Although a number of materials have been proposed and tested heretofore, no entirely satisfactory material from which to form the inner layer (next to the liquid) has been uncovered. To be satisfactory as an inner liner for self-sealing liquid containers, and

particularly when used in gasoline tanks on aircraft, the material must possess good strength, elasticity, and capability of receiving bullet punctures without tearing, must not be degraded by the liquid contents of the container, must not contaminate the liquid, and must retain these properties over a wide temperature range,

The materials previously used as the inner liner r liquid-containing layer suffer from one or more disadvantages. Neoprene, which is the polymerization product of 2-chlorobutadiene and which is highly resistant to the solvent action of I oils and of many liquids, is probably the most satisfactory material previously used, but is swelled by a number of fluids and particularly by the aromatic hydrocarbons. The resinous materials proposed are lacking in flexibility and if the fuel and the resin inner liner slowlyreturns to its original condition of stifiness. This invention has as an object an improved fuel container. A further object'is a self-sealing container provided with'an inner liner which is durable andsubstantially impervious to the liquids for which the container is adapted to be used. A furtherobject is a self-sealing container having aninner liner which possesses the flexibility, strength, durability, freedom from embrittlement on agin and other properties which particularly adapt the container for-use on aircraft.

after.

The above 'ductlon of anjimproved fuel tank or container Other objects will appear herein areaccomplished by'the ii o soxqw the presentpurpose but are unlike 2 and more particularly of a self-sealing fuel tank in which the fuel-contacting element of the tank is composed of a synthetic olyamide of the kind more fully described hereinafter.

The polyamides with which this invention is concerned are highmolecular weight polymers of the general type described in U. S. Patents 2,071,250, 2,071,253, 2,130,948 and 2,224,037. Polyamides of this kind, generally speaking, comprise the reaction product of a linear polymer-' forming composition, for example, one consisting essentially of bufunctional reacting material, which comprises in substantial amount molecules containin two amide-forming groups each of which is complementary to an amide-forming group in other molecules in said composition. These polyamides as described above or as otherwise identiiied hereinaftercan be obtained, for example, by self-polymerization of monoaminomonocarboxylic acid, or by reacting a diamine with a dibasic carboxylic acid in substantially equimolecular amounts, it being understood that reference herein to the amino acids, diamines and dibasic carboxylic acids is intended to include the equivalent amide-forming derivatives of these reactants. In the polymers made with these reactants the average number of carbon atoms separating the amide groups is at least two.

I have found that those polymers of the above mentioned general type, which are obtained by including glycols.or other .bifunctional esterforming reactants with the polyamide-forming reactants, when used as the inner layer of a selfsealing fuel tank presents several valuable advantages that have not been realized heretofore in the previously made fuel containers of this 'hexamethylene diisocyanate with the polyesteramide-formin composition, for example with a mixture of amino acid and glycol, or with a mixture of diamine, dibasic carboxylic acid and glycol. The mention. of diiocyanates herein is intendedto include also the corresponding diisothiocyanates. These diisocyanates modified polyester-amides are best obtained by heating the diisocyanate compound with the low molecular weight polyester-amide obtained by stopping the olymerization reaction before completion.

' The ester-amide polymers described above, in addition to being unusually strong and tough, are

rubber-likeinsome respects to the degree rerubber in that they are substantially unaffected by gasoline or other hydrocarbon fuels. They have a high and permanent flexibility without plasticizer and hence are not subject to embrittlement through exudation or solvent extraction of the plastlcizer. I have found that the polyamides of these characteristics are of peculiar value as the inner liner of self-sealing tanks which are exposed to bullet puncture. Inner liners composed of these polymers, in addition to unusual toughness and permanent flexibility which adapts them to aircraft use through resistance to bursting areespecially suited for use on fighting aircraft due to the capability of the inner liner of withstanding gun fire without mutilation beyond the perforation caused by the bullet.

An embodiment of my invention is shown in the accompanying drawings in which Fig. 1 is a perspective view of-the removable framework around which the cell consisting of the inner layer or liner and intermediate swelling layer is constructed;

Fig. 2 is a perspective view of the container obtained by applying the above mentioned inner and sealing layers to the framework;

"Fig. 3 is a perspective view showing the completed cell; and

Fig.4 is a. sectional view showing the different layers of material making up the cell.

A convenient method for practicing my invention is as follows:

A cubical framework such as shown in Fig. l of the desired size, which in the present embodiment is about 24 inches on each edge, is constructed of light wooden members I suitably mortised and fastened together with small wire nails or brads 2. A calendered sheet of the polyamide composition is then wrapped continuously around the four sides and the ends joined by a solvent bond. Two sheets of this material, indicated by the numeral 3 in Fig. 4, and 26 inches on each edge, are then cut and used to cover the top and bottom of the cubical framework, lapping the edges over the sides, and joining by a solvent bond. The bonding of the edges is efiected by softening the edges of the sheets with an equivolume mixture of ethanol and ethylene dichloride; and then holding the edges together under a light pressure until the joint has set.

The entire outer surface is then wet with the above ethanol-ethylene dichloride mixture, and

while the surface is tacky, wood fiouris dusted on, as an intermediate fibrous material to which a, resilient layer of a plasticized neoprene 4 is cemented with neoprene cement consisting of a solution of neoprene in a solvent, this resilient layer being wrapped around the entire hollow cube precisely as the first layer was put on. The neoprene-to-neoprene joints are sealed with neoprene cement. It is the primary purpose of this resilient layer to expand or stretch mechanically under the deforming action of the puncturing object and then by its resilience to return to its original position and mechanically close up the puncture produced, so reducing leakage to a minimum. Under certain conditions softening action.

of the contents of the container on this layer has a further beneficial effect in closing the perforation. This resilient layer is coated with a neoprene cement and then covered with a layer of unvulcanized rubber 5 which is capable of swelling under the action of hydrocarbon solvents.

This is then coated with rubber cement and a layer of vulcanized rubber 8 applied which serves 4 as an outer protective elastic abrasion resistant covering for it.

A hole 6, 4 inches in diameter, is then cutin the top and a hole I, /2 inch in diameter, is cut for the fuel outlet. This hole is best placed in the bottom end of the cell to insure complete drainage, but for easier illustration in the drawing it is shown in one of the side walls near the bottom. By reaching through the larger hole in the top, the wood framework is dismantled and removed through the hole. A fuel line communicates through the hole I with the cell contents by means of a tube 9 terminating in a flange portion H! which is cemented around the hole 1 either on the outer or inner layer or between the layers. The flange and tube can be of the same material as the inner layer or made of rubber with the flange and interior walls of the tube coated with the polyamide. A similar flange ll having a fuel inlet consisting of an upright portion l2 provided with a cap I3 is cemented over the hole 6.

It is to be understood that this invention of self-sealing containers and not with the particular arrangement and kind of the sealing and protective layers in addition to the inner polyamide layer. Another useful form of cell is one in which the layer next to the polyamide inner layer is a swelling layer of raw rubber and the subsequent layers in the order named are a layer of sponge rubber, a second swelling layer of raw rubber and an outer protective covering of leather. Strong flexible containers of the nonsealing type and of particular utility on aircraft are also obtained by the practice of this invention.

trated the outer and inner walls without substantially any leakage. Examinationof the inner wall after the firing test showed no ripping, in

contrast to the severe rips and tears produced hexamethylenediammonium adipate, and

parts of water (added to assist homogenization) is heated for 32 hours at 200 C. and 760 mm. pressure in a stirred reactor. The water added and that formed in the course of the reaction is taken off through a suitable condenser system. The product at this stage is light colored, waxlike material. Ninety-four parts of this wax is melted at C. in a jacketed, heavy duty mixer and 6 parts of hexamethylene diisocyanate is slowly added over a period of 15-20 minutes to facilitate conversion of the low molecular weight wax-like product to a high molecular weight polymer. The temperature is then raised to C. and mixing continued for an additional 15 minutes. The product at this stage is a very tough, fusible material, insoluble in most organic solvents, including aromatic and aliphatic hydrocarbons and their mixtures. Forty-eight parts of this polymenare then compounded on rubber rolls with 39.5 parts of lithopone, 8.2 parts of is concerned with improvements in the known types amazes amides are preferred. These polymers are obtained by including with the, polyamide-forming reactants other linear polymer-forming reactants such as glycols, amino alcohols, hydroxy acids or derivatives from which these reactants may be formed during the course of condensation. Examples of such superpolymers are those obtained by the reaction of hexamethylenediammonium adipate (the salt formed by contact oh the diamine with the dibasic acid) with adipic acid and ethylene glycol; hexamethylenediammonium adipate with adipic acid and 2,2-dimethyl propylene glycol; adipic acid with monoethanolamine and ethylene glycol; hexamethylenediammonium adipate with hydroxyacetic acid; hexamethylenediammonium sebacate with sebacic acid and ethylene glycol; and decamethylenediammonium sebacate with sebacic acid and butylene glycol. The polyesteramides are also obtained by reacting amino alcohols and dicarboxylic acids either in the presence or absence of glycols, diamines, amino acids and hydroxy acids.

The formation of the polyester-amide composition into sheet material. may be effected by several methods which include sheeting by calendering, by cake pressing and slicing, by pressing to a sheet, by extrusion, by molding under the influence of heat and pressure, and in the case of soluble species, by casting a film from suitable solvents. The sheeting so formed, which may or may not be supported by a backing, can then be brought into the form of useful articles by cutting to pattern and fabricating, using adhesives, solvent bonds, heat seals, or stitching, alone or in any combination. As adhesives, solutions in suitable solvents of the same species ofv polymer as that used in the sheeting being bonded may conveniently be employed.

The particular solvent used for making the adhesive or as a medium for forming the solvent bond will depend upon the particular polymer under consideration. Examples of specific solvents which may be employed include methanolchloroform mixtures, ethanol-ethylene dichloride mixture, and ethanol-acetone water mixtures with interpolymers of hexamethylenediammonium adipate, ethylene glycol and adipic acid. In general, the more volatile solvents are preferred to the less volatile ones.

Bonding of the polyamide inner. liner to adjacent laminae of the fluid container may be accomplished by the use of mutual cements or by the use of solvents which induce tack on the surface of both materials, or by the procedure previously outlined through the use of an intermediate fibrous material which will permit the use of specific cements for each laminae. This latter method is particularly advantageous.

The linear polymers described herein can be used alone but their utility for the present purpose is enhanced by the fact that they can be compounded easily with inert modifying ingredients and with fillers. These fillers, when inert,

may be mixed with the ingredients from which the polymeric material is to be formed before mer in a. number of ways.

condensation is carried out; or the fillers may be worked into the finished polymer, either on compounding rolls, in heavy duty mixers, or by adding to solutions of the polymer. The weight of filler used may be varied between wide limits, depending on the nature of the polyamide used and the properties desired in the final product. The modifying agent can be mixed with the poly- In some cases the mixing can best be carried out in solution, while in other instances the operation is best conducted by softening the polymer" by heat and milling in the other ingredients. In somecases it may be desirable to incorporate the modifiers during or prior to the polymerization of polyamides.

Other modifiers which can be incorporated into the polyamide for improving durability, ease in working the material on fabricating equipment, or for other purposes include waxes, resins, pigments, colors, stabilizers, fillers, extenders, and antisticking agents. Resins may be added to improve the hardness of the surface, improve water resisitance, improve milling properties, facilitate the take up of other modifiers. Examples of suitable resins are synthetic resins, for example, polyvinyl acetate, natural resins and their derivatives, for example, rosin, hydrogenated rosin, ester gum, hydrogenated ester gum, shellac gum kauri, copal, etc. Fillers which act to improve flow on the 'milling rolls include chalk, clay, whiting, vermiculite, mica, asbestos, silica, leather shavings, cellulose and cellulose derivatives, etc. Pigments suitable for incorporation include zinc oxide, carbon black, 'lithopone, blanc fixe, lakes, azo pigments, rubber colors, Prussian blue, chrome green, titanium oxide, iron oxide, lithol red, zinc sulfide, antimony sulfide, iron blue, and the phthalocyanines. These pigments may be used alone or in combination. It will further be understood that these pigments may likewise serve as fillers and extenders. As antisticking agents, that is agents used in preparing the calendered sheets to facilitate removal of the sheeted material from the rolls, there can be used low melting waxes such as paraffin, carnauba, montan, and Opalwax; esters such as di'amyl phthalate, dicyclohexyl phthalate, dioctyl phthalate, dilauryl phthalate, glycol maleate, butyl sebacate; ethers such as diethylene glycol dicresyl ether, ethylene glycol monobenzyl ethers, and ethylene glycol monophenyl ether; acids such as oleic and stearic acid; salts such as zinc stearate, magnesium stearate, aluminum stearate, sodium stearate, dibutyl ammonium oleate, and palm oil.

The polyamide sheeting is used in thicknesses which will retain the requisite mechanical strength and which will provide the required impermeability to the fuel, but which will not un'- desirably increase the weight of the tank.

The material used in the intermediate solvent expanding layer will be governed by the swelling action of the liquid for which the container is closed herein are, for the reasons pointed out above, of unusual value for use as the fuel tanks of vehicles subject to gun fire. The present flexible fuel containers are highly resistant to the leaks caused by vibration which often occur from this cause in metal tanks. The insertion of the present flexible self-sealing cells in a metal container is, however, not precluded, although this practice is not usual. This invention also makes possible the manufacture of improved flexible fuel tanks of the non-sealing type. Such tanks may, for example, be constructed from a fabric coated on one or both sides with a polyester-amide, or they may be constructed from heavy unsupported polyester-amide sheeting without fabric backing. Such cells are usually supported in a metal container'since their cell walls have little mechanical strength.

The properties of inertness to both aliphatic and aromatic fuels, high strength, low temperature toughness and permanent resilience together with the absence of tearing on bullet puncture and other advantages previously pointed out make the composite self-sealing container of this invention particularly valuable in all applications where a container is subject to puncture and it is important that the rupture so created be sealed as rapidly as possible. The present fuel cells are especially useful in military and naval aircraft where the fuel container may be punctured by machine gun or anti-aircraft fire and the craft subsequently put out of action either by a deficiency of fuel or from an explosion or firing of the leaking fuel. A further advantage of the present fuel tank resides in the fact that the 'polyamide inner liner can, if necessary, be easily quired shape by conventional techniques. Thus the polyamlde is readily converted into the desired sheet form and the'complete cell is made by a simple procedure.

As many apparently'widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to layer of expansible material comprising plasticized neoprene which is positioned intermediate said first two mentioned layers and which is adapted to close perforations formed through said layer of expansible material, said polyesteramide being the high molecular weight tough and rubber-like reaction product of an hexamethylene diisocyanate with the lower molecular weight polyester-amide comprising the reaction product of adipic acid, ethylene glycol, and hexamethylene diammonium adipate.

HAROLD S. HOLT.

REFERENCES CITED The ollowing references are of record in the file of this patent:

' UNITED STATES PATENTS Number Name Date 2,137,686 Habgood Nov, 22, 1938 2,333,914 Berchet Nov. 9, 1943 2,282,827 Rothrock May 12, 1942 2,252,554 Carothers Aug. 12, 1941 1,779,397 Kraft Oct. 21, 1930 1,297,305 Thacher Mar. 11, 1919 

